This page (for 2.2) should be also fixed:
https://www.percona.com/doc/percona-xtrabackup/2.2/xtrabackup_bin/incremental_backups.html
This page (for 2.2) should be also fixed:
https:/ /www.percona. com/doc/ percona- xtrabackup/ 2.2/xtrabackup_ bin/incremental _backups. html